Get object data for previous frame in driver?
In a scene with an animated plane (along x-axis), and a Cube with a driver added to z-rotation the following python snippet produces the same value as the default var in the driver. Where the evaluate function takes the frame as parameter.

import bpy

for fcurve in bpy.data.objects['Cube'].animation_data.drivers:
    print(fcurve.evaluate(54))